Polyelectrolytes for an improved aquaporin embedded top layer for next generation

IntroductionAn emerging separation and desalination technology that shows great potential is forward osmosis (FO). FO uses osmotic pressure gradients to transport water across a semipermeable membrane. These membranes are usually based on reverse osmosis (RO) membranes, which lack, however, suitability for FO applications [1]. A way to create new membranes truly optimized for FO, is by self-assembly of oppositely charged polyelectrolytes (PEs) on the surface of a porous ultrafiltration support membrane. In this so-called Layer-by-Layer (LbL) assembly, the support membrane is alternatively exposed to polycations and polyanions [3]. Such a PEM coating is easily applied on all geometries. In this study, the focus will be to create a PEM based membrane suitable for FO. PEMs will be made as dense as possible by means of crosslinking and the use of different kinds of PEs. Subsequently the layer will be characterized and tested on its FO performance. To make these membranes more even more suitable, aquaporin containing vesicles can be incorporated within the PEM layer to enhance the permeation and rejection properties [2].

StudyCreating more intrinsic bonds will increase the rejection properties of an active membrane layer. Crosslinking is a manner to create more intrinsic bonds and can easily be done by heat or a catalyst. Many moieties of PEs are amines or carboxylic acids which can easily be crosslinked, as shown in Figure 1.Crosslinking of PEMs has already shown to be a promising way to create an active layer capable of retaining salts [4]. For FO purposes, the layer has to be as dense as possible in order to cope with highly concentrated saline streams. In order to control the layer density, different materials can be used that influence the intermolecular distance.In this MSc project, different types of crosslinking techniques and materials will be evaluated. Materials will vary from aliphatic, branched, to aromatic structures while controlling and monitoring the performance of the membrane.

MethodsPEMs can be made by dip-coating silicon wafers or membranes in a solution containing a certain polyelectrolyte. The growth and properties of these multilayers can be monitored by using techniques like reflectometry, ellipsometry, contact angle, and

Crosslinking can be done catalyzed or non- catalyzed. Non-catalyzed reactions take place under the influence of heat. To see if crosslinking has taken place, the layer will be characterized using FTIR and NMR measurements.The knowledge obtained from model surfaces (silicon wafers) will be translated to hollow fiber membranes. The membranes will be coated and crosslinked under the same conditions as the model surfaces and will be tested on their performances in forward osmosis operating conditions.